This invention relates to a novel process for producing a 1,4,5,8-naphthalene tetracarboxylic acid which is a well-known intermediate product for dye, pigment, resins and the like.
In the prior art, 1,4,5,8-naphthalene tetracarboxylic acid (hereinafter referred to as merely "NTCA") has been produced by the halogenation of pyrene which can be produced from a coal tar and by a two-step oxidation with reagents (Ullmann's Encyclopedia of Industrial Chemistry, Vol.A5, p.249). In an alternative method, NTCA has been conventionally synthesized by following steps: using 1,2 dihydroacenaphthylene obtained from coal tar as a starting raw material: adding acyl radicals such as carbon to the 5,6 position: and then by hydrolyzing or oxidizing the result.
A drawback of the halogenation of pyrene and the two-step oxidation with reagent is the difficulty of obtaining pyrene as a raw material. Besides these processes consume a large amount of acid and alkali. Other technical problems include poor yield, and high cost of 1,2-dihydroacenaphthalene as a starting raw substance in the synthesis.